1. Field of the Invention
The invention relates to the preparation and application of a new class of metal complexes whose general formula are depicted below: 
wherein R1 represents substituted and nonsubstituted phenyl (Ph), pyridyl, pyrimidinyl, pyrazinyl, pyrrolyl, pyrrolinyl, imidazolyl, naphthyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, indenyl, indolyl, 4-isobenzazolyl, indoleninyl, anthracyl, phenanthrolinyl or pyrrolidyl, piperidyl, cycloalkyl groups or any combination thereof. R2 represents substituted and nonsubstituted phenyl (Ph), naphthyl, anthracyl, indenyl, cycloalkyl groups or any combination thereof. Py represents substituted and nonsubstituted pyridyl, pyrimidinyl, pyrazinyl, pyrrolyl, pyrrolinyl, imidazolyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, indolyl, 4-isobenzazolyl, indoleninyl, phenanthrolinyl, pyrrolidyl, piperidyl or any combination thereof. X and Y can be the same or different, and represent hydrogen (H), hydroxyl (OH), alkyl (R), alkoxy (RO), cycloalkyl, halogen, nitro groups or any combination thereof. Z represents a hydroxyl (OH) or negative oxygen ion (Oxe2x88x92). W represents an anion such as a halide, nitrate, sulfate, acetate, trifluoroacetate, trifluoromethanesulfonate, tetrafluoroborate, hexafluorophosphorate, perchlorate, oxalate, carbonate or any combination thereof. P represents a hydrogen atom (H) or negative charge (xe2x8ax96). M represents a metal ion from groups IB, VB, VIB, VIIB or VIII of the periodic table of the elements. This invention also relates the preparation of aryl methyl ketones via oxidation of ethyl arenes using one of these complexes as catalyst, and using molecular oxygen as oxidant. The improved aryl methyl ketone selectivity and improved conversion of ethyl arene provided by this invention are particularly suitable for the industrial scale production of alkyl aryl ketone compounds.
2. Prior Art
There are several methods for preparing aryl methyl ketones. Among them, the preparation of the structurally simplest acetophenone, which is produced commercially on a large scale, has been most extensively studied. The most commonly used method of preparing acetophenone is via the oxidation of ethylbenzene using cobalt acetate or cobalt cycloalkanecarboxylate type compounds as catalyst, bromide compounds as a co-catalyst in acetic acid solvent, and molecular oxygen or air as the oxidant. A significant disadvantage of this method is the strongly corrosive nature of the bromide compounds and the acetic acid solvent. This type of reaction usually requires the use of expensive corrosion-resistant equipment. Another disadvantage of this method is the low effective utilization of the reactor due to the involvement of a large quantity of the acetic acid solvent. The third disadvantage of this method is the high cost associated with the separation and recycling of the acetic acid solvent.
Yasutaka Ishii (Journal of Molecular Catalysis A: Chemical 117, pp 123-137, 1997) reported a method for the oxidation of ethylbenzene to acetophenone by using N-hydroxyphthalimide as a catalyst, cobalt acetoacetonate as the co-catalyst, and molecular oxygen as the oxidant. The acetophenone product was obtained with high yield. However, this reaction still needed to use acetic acid as solvent, and therefore had corrosion problem. The amount of co-catalyst used in the reaction system was very high (10%), thus making the catalyst system expensive.
Lei et al. reported a method for oxidizing alkyl benzene in the absence of solvent (Chinese Chemical Letters Vol. 3, No. 4, pp 267-268, 1992). In this reaction 2,2xe2x80x2-bipyridyl coordinated ruthenium complex was used as catalyst, and molecular oxygen or air was used as oxidant. The highest ethylbenzene conversion was only 43.8%, and the selectivity for acetophenone was only 74%.
Lei et al. also reported another method for oxidizing alkyl benzene (Chinese Chemical Letters Vol. 4, No. 1, pp 21-22, 1993) without the use of any solvent. The method employed Fe-(2,2xe2x80x2-bipyridyl) or Fe-(1,10-phenanthroline) as the catalyst and molecular oxygen as oxidant. When 5 mL of ethylbenzene was oxidized in the presence of 2 mg of the catalyst, the conversion of ethylbenzene was only 11.4-34.6% after 3.5 hours. The selectivity for acetophenone was only 66.2-89.8%.
When using either one of Lei""s methods to prepare acetophenone, one cannot get both high turnover frequency and good acetophenone selectivity. Taking the best result from Chinese Chemical Letters Vol. 4, No.1, pp 21-22, 1993 as an example, when the conversion of ethylbenzene was 25.3% (turnover frequency 686 mol/mol catalyst-hour), the selectivity for acetophenone was 89.8%. However, the selectivity for acetophenone dropped to 67.22% when the ethylbenzene conversion was increased to 34.58% (turnover frequency 1010 mol/mol catalystxc2x7hour). Among the reported methods for substituted ethylbenzene oxidation and the oxidation of other ethyl arenes (such as the oxidation of halo-ethylbenzene, methyl-ethylbenzene, methoxy-ethylbenzene, nitro-ethylbenzene or ethyl-naphthalene, etc.), normally a peroxide compound was used as the oxidant. The use of molecular oxygen as oxidant has not been reported.
It is an object of the present invention to overcome or a substantially ameliorate at least one of the above disadvantages.
It is another object of the present invention is to provide a highly effective method for the selective preparation of methyl aryl ketones via the oxidation of ethyl arenas using molecular oxygen as the oxidant without the use of any solvent.
This invention provides the methods for the preparation of three classes of complexes with the general formula shown below: 
wherein R1 represents substituted and nonsubstituted phenyl (Ph), pyridyl, pyrimidinyl, pyrazinyl, pyrrolyl, pyrrolinyl, imidazolyl, naphthyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, indenyl, indolyl, 4-isobenzazolyl, indoleninyl, anthracyl, phenanthrolinyl or pyrrolidyl, piperidyl, cycloalkyl groups or any combination thereof R2 represents substituted and nonsubstituted phenyl (Ph), naphthyl, anthracyl, indenyl, cycloalkyl groups or any combination thereof. Py represents substituted and nonsubstituted pyridyl, pyrimidinyl, pyrazinyl, pyrrolyl, pyrrolinyl, imidazolyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, indolyl, 4-isobenzazolyl, indoleninyl, phenanthrolinyl, pyrrolidyl, piperidyl or any combination thereof. X and Y can be the same or different, and represent hydrogen (H), hydroxyl (OH), alkyl (R), alkoxy (RO), cycloalkyl, halogen, nitro groups or any combination thereof. Z represents a hydroxyl (OH) or negative oxygen ion (Oxe2x88x92). W represents an anion such as a halide, nitrate, sulfate, acetate, trifluoroacetate, trifluoromethanesulfonate, tetrafluoroborate, hexafluorophosphorate, perchlorate, oxalate, carbonate or any combination thereof. P represents a hydrogen atom (H) or negative charge (xe2x8ax96). M represents a metal ion from groups IB, VB, VIB, VIIB or VIII of the periodic table of the elements.
This invention also includes the use of these complexes as catalysts for oxidizing ethyl arenes to aryl methyl ketones. The catalysts have the advantages of high ethyl arene conversion, high turnover frequency as well as high selectivity for the aryl methyl ketone products.
The purpose of this invention is to provide a method for the selective preparation of methyl aryl ketone via oxidation of ethyl arene using molecular oxygen as the oxidant without the use of any solvent.
The method of the preferred embodiment includes carrying out the reaction at 50-300xc2x0 C. at any pressure between atmospheric pressure and 10 MPa, and reacting ethyl arene with a catalyst and an oxygen-containing gas such as air or oxygen-enriched air. The concentration of the catalyst in the reaction system is in a range from 10xe2x88x926 to 5.0 mol/L, and the catalyst is a complex of the following general formula or a mixture of these species: 
wherein R1 represents substituted and nonsubstituted phenyl (Ph), pyridyl, pyrimidinyl, pyrazinyl, pyrrolyl, pyrrolinyl, imidazolyl, naphthyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, indenyl, indolyl, 4-isobenzazolyl, indoleninyl, anthracyl, phenanthrolinyl or pyrrolidyl, piperidyl, cycloalkyl groups or any combination thereof. R2 represents substituted and nonsubstituted phenyl (Ph), naphthyl, anthracyl, indenyl, cycloalkyl groups or any combination thereof. Py represents substituted and nonsubstituted pyridyl, pyrimidinyl, pyrazinyl, pyrrolyl, pyrrolinyl, imidazolyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, indolyl, 4-isobenzazolyl, indoleninyl, phenanthrolinyl, pyrrolidyl, piperidyl or any combination thereof. X and Y can be the same or different, and represent hydrogen (H), hydroxyl (OH), alkyl (R), alkoxy (RO), cycloalkyl, halogen, nitro groups or any combination thereof. Z represents a hydroxyl (OH) or negative oxygen ion (Oxe2x88x92). W represents an anion such as a halide, nitrate, sulfate, acetate, trifluoroacetate, trifluoromethanesulfonate, tetrafluoroborate, hexafluorophosphorate, perchlorate, oxalate, carbonate or any combination thereof. P represents a hydrogen atom (H) or negative charge (xe2x8ax96). M represents a metal ion from groups IB, VB, VIB, VIIB or VIII of the periodic table of the elements. The invention also includes the preparation of these catalysts. This invention also relates the preparation of aryl methyl ketones via oxidation of ethyl arenes using one of these complexes as catalyst and molecular oxygen as the oxidant. The improved aryl methyl ketone selectivity and improved conversion of ethyl arene provided by this invention are particularly suitable for the industrial scale preparation of aryl ketone compounds.
When X=Y=H, R1=R2=Ph, the ligand in complex (I) is N-phenylbenzohydroxamic acid, abbreviated as HPBHA, and the complex in general formula (I) is N-phenylbenzohydroxamate anion coordinated M complex, abbreviated as M(PBHA)n. PBHA represents the deprotonated form of HPBHA. 
When X=Y=H, R1=Ph, Py=pyridyl, Z=OH, and the carbonyl group is at the ortho, meta or para-position relative to the pyridine nitrogen atom, the ligand in the general formula (II) is N-phenyl-2-pyridinecarbonylhydroxamic acid, N-phenyl-3-pyridinecarbonylhydroxamic acid or N-phenyl-4-pyridinecarbonylhydroxamic acid, abbreviated as o-HPPHA, m-HPPHA or p-HPPHA, respectively. The complex in general formula (II) is N-phenyl-2-pyridinecarbonylhydroxamate anion coordinated M complex, abbreviated as M(o-PPHA)n, N-phenyl-3-pyridinecarbonylhydroxamate anion coordinated M complex, abbreviated as M(m-PPHA)n or N-phenyl-4-pyridinecarbonylhydroxamate anion coordinated M complex, abbreviated as M(p-PPHA)n. PPHA represents the deprotonated form of HPPHA. 
In this invention, the X group in the general formula (II) and (III) can be at any possible position in the pyridine ring, that is, the 3-, 4-, 5- or 6-position of the pyridine ring. 
When X=Y=P=H, R1=Ph, Py=2-pyridyl, the ligand in general formula (III) is N-phenyl-2-pyridinecarboxamide, and is abbreviated as HPPA or its deprotonated anion form PPA. The complex in general formula (III) is N-phenyl-2-pyridinecarboxamide or its anion coordinated M complex, and is abbreviated as M(PPA)n (M=Co, n=3; M=Cu, n=2), M(HPPA)(PPA)2 (M=Ni), M(HPPA)2W2 (M=Mn, W=Cl) or M(HPPA)(PPA)W2 (M=Ru, W=Cl) etc. 
This description of certain particular catalyst formulae is by no means intended to limit the scope of this invention to the specific complexes so described. Any complex meeting the general description claimed above is within the scope of this invention.
The catalyst used in this invention can be prepared according to the following procedure, which is presented as an example only. Any other similar procedures also fall within the scope of this invention:
(1) The preparation of catalyst of general structure (I): A ligand in general structure (I) is dissolved in an alcohol solvent so that the concentration of the ligand is from 10xe2x88x923 to 1.0 mol/L. A suitable concentration is from 0.05 to 0.5 mol/L. With the temperature at 20 to 150xc2x0 C. (most favorable temperature is 40 to 100xc2x0 C.), a solution containing metal ion M with the concentration of 10xe2x88x922 to 1.0 mol/L (the most favorable concentration is 0.1 to 0.4 mol/L) is added to the ligand solution. The amount of metal ion is such that it makes the ligand-to-metal molar ratio in a range of 1 to 5 (most favorable ratio is in a range of 2 to 3). The precipitate is filtered off and the solid is washed with de-ionized water until it is free of acid. A complex of general structure (I) can thus be obtained.
The alcohol can be any aliphatic alcohol of C1-C5, for example, methanol, ethanol, n-propanol, i-propanol, all the isomers of butanol, and all the isomers of pentanol. Among these, the more favorable are ethanol or n-propanol and the most favorable is ethanol.
The metal ion solution is an aqueous or alcoholic solution of a soluble salt of metal. For example, the aqueous or alcoholic solution of a metal halide, nitrate, sulfate, acetate, trifluoroacetate, trifluoromethanesulfonate, tetrafluoroborate, hexafluorophosphorate, perchlorate, oxalate, carbonate or any combination thereof.
The temperature for drying the complex is from room temperature to 200xc2x0 C. and the most favorable temperature range is 80 to 150xc2x0 C.
(2) The preparation of catalyst of general structure (II): the ligand for preparing the complex is dissolved in alcohol to give a solution concentration of about 0.02 to 2 mol/L (The more favorable concentration range is 0.05 to 1.0 mol/L). The alcoholic or aqueous solution containing M ion is added at 10 to 150xc2x0 C. (preferably at 40 to 100xc2x0 C.) with stirring. The mixture is reacted for 0.2 to 5 hours (preferably 0.5 to 3 hours). The concentration of the M ion in the stock solution is about 0.05 to 2 mol/L (preferably 0.1 to 1.0 mol/L). The amount of added M ion is such that the molar ratio of ligand-to-metal ion is between 1:1 and 4:1 (preferably between 2:1 and 3:1). The precipitate thus formed is filtered off, washed with 95% alcohol until it is acid-free, and dried to give a complex of general structure (II).
The alcohol in the above mentioned preparation can be any aliphatic alcohol of C1 to C5, such as methanol, ethanol, n-propanol, i-propanol, all isomers of butanol, and all isomers of pentanol. The more favorable are ethanol or propanol, and the most favorable alcohol is ethanol.
The alcoholic or aqueous solution of the metal ion may be the alcoholic or aqueous solution of the metal salt, such as the alcoholic solution of a metal halide, nitrate, sulfate, acetate, trifluoroacetate, trifluoromethanesulfonate, tetrafluoroborate, hexafluorophosphorate, perchlorate, oxalate, carbonate or any combination thereof.
The temperature for drying the ligand is room temperature to 180xc2x0 C. (preferably 50 to 150xc2x0 C.).
(3) The preparation of catalyst of general formula (III): the ligand for preparing the complex is dissolved in an alcohol to make a solution of a concentration in a range of 0.05 to 2 mol/L (preferably 0.1 to 1.0 mol/L). An aqueous solution containing M ion and ammonia is added with stirring and reacted for 0.5 to 4 hours (preferably 1 to 2 hours). In the aqueous or alcoholic solution of metal ion and ammonia, the concentration of metal ion is 0.02 to 2 mol/L (preferably 0.05 to 1.0 mol/L). The metal ion concentration is such that the molar ratio of ligand to metal ion is between 1:1 and 5:1 (preferably between 2:1 and 3:1). The concentration of ammonia is 0.1 to 30 mol/L (preferably 0.5 to 10 mol/L). The thus formed precipitate was filtered off, washed until it is acid free using de-ionized water, and dried to give a complex of general formula (III).
The alcohol in the above mentioned preparation can be any aliphatic alcohol of C1 to C5, such as methanol, ethanol, n-propanol, i-propanol, all isomers of butanol, and all isomers of pentanol. The more favorable are ethanol or propanol, and the most favorable alcohol is ethanol.
The mixed aqueous or alcoholic solution of metal ion and ammonia can be made from any soluble salt of the metal ion, such as metal halide, nitrate, sulfate, acetate, trifluoroacetate, trifluoromethanesulfonate, tetrafluoroborate, hexafluorophosphorate, perchlorate, oxalate, carbonate or thereof, and aqueous ammonia.
The temperature for drying the product is room temperature to 200xc2x0 C. (preferably 70 to 150xc2x0 C.).
In this invention, the catalyst concentration in the reaction system is 10xe2x88x926 to 5.0 mol/L (preferably 10xe2x88x925 to 10xe2x88x922 mol/L).
The reaction temperature is 50 to 300xc2x0 C. (preferably 100 to 150xc2x0 C.).
The oxygen pressure in the reactor can be ambient pressure to 10 MPa, but for economic reason preferably ambient pressure to 3 MPa, and most preferably ambient to 1.5 MPa.
The reaction time varies with the variation of the catalyst concentration, reaction temperature and reaction pressure higher reaction temperature gives faster turnover frequency and the reaction requires shorter time to reach a specific conversion level. The turnover frequency is higher under higher reaction pressure. Higher turnover frequency and shorter reaction time needed to reach a specific conversion is also achieved by using higher catalyst concentration. For the convenience of operation, the usual reaction time is in a range of 0.5 to 20 hours, typically 2 to 12 hours.
The oxygen-containing gas used in the reaction may be pure oxygen or a gas containing O2 such as air or oxygen-enriched air with other gaseous contents that do not affect the reaction. The oxygen content of the oxygen-containing gas should be above 20% (V/V) or higher. The other gaseous contents, which do not affect the reaction, may include the group 0 inert gases of the periodic table, nitrogen or carbon dioxide or any mixture of them. The preferable oxygen-containing gases are pure oxygen, oxygen-enriched air or air.
In the preferred embodiment, the ethyl arene is any arene bearing an ethyl group as a substituent on the aromatic ring. For example, substituted or unsubstituted ethylbenzene or ethylnaphthalene. The favorable ethylarenes include ethylbenzene, ethylnaphthalene, substituted ethylbenzene or ethylnaphthalene bearing one or several halo, methyl, methoxy, nitro group or any combination of thereof as the substituent. They are oxidized to acetophenone, halo acetophenone, methyl acetophenone, methoxy acetophenone, nitro acetophenone, methyl naphthyl ketone or any methyl aryl ketone bearing any combination of the substitutes. The more favorable ethyl arenes include ethylbenzene, halo ethylbenzene or methoxy ethylbenzene.
In this preferred embodiment, the catalyst can be readily separated from the reaction system through distillation of the reaction mixture, and the separated catalyst can be recycled and reused.
Compared with previously known solvent free methods, the method of this invention can give higher conversion of ethylarene and high yield of the desired methyl aryl ketone product. For example, using ethylbenzene to produce acetophenone, acetophenone selectivity can be as high as 93% even when the ethylbenzene conversion is as high as 63%.
In addition, high acetophenone selectivity can still be obtained even when running the reaction at high turnover frequency. For example, using the method in this invention, acetophenone selectivity can be 90% when the turnover frequency is as high as about 1500 mol/mol catalyst-hour.